PROJECT SUMMARY We cloned TIM 3 as a molecule differentially expressed on IFN-g producing T cells and has emerged as a major inhibitory molecule necessary for the termination of effector T cell responses. Tim 3 expression is increased on effector T cells in human chronic viral infections and cancers, rendering them dysfunctional. In contrast, in human autoimmune diseases, there is loss of Tim 3 expression on effector T cells, rendering them highly pro- inflammatory and pathogenic. Because of its role in T cell exhaustion, Tim 3 is being targeted in multiple clinical trials for cancer. Tim 3 is also expressed constitutively on dendritic cells (DCs), however, the role and function of Tim 3 on DCs is not well understood and this is especially important to understand, in the view of clinical trials that are underway with anti-Tim 3 antibodies. As in T cells, Tim 3 is co-expressed in DCs with its adapter protein Bat-3, where Bat-3 acts as a molecular ?gate- keeper?, that restricts Tim 3 signaling and function. To understand the function of Tim 3 in DCs, we have generated conditional ?knock-out? mice of both Tim 3 and Bat-3 in DCs. Initial studies indicate that unrestricted signaling of Tim 3 in the absence of Bat-3, makes Bat-3-deficient DCs tolerogenic such that they do not effectively induce inflammatory T cell responses and the mice are resistant to development of autoimmunity. Based on our preliminary data, we hypothesize that unabated Tim 3 signaling in DCs promotes generation of tolerogenic DCs. To address this hypothesis, we propose two specific aims: 1. Determine how the Tim 3/Bat-3 interaction regulates development of tolerogenic DCs. We have observed that unopposed signaling of Tim 3, by deleting Bat-3, specifically in DCs inhibits development of multiple autoimmune diseases including Experimental Autoimmune Encephalomyelitis (EAE) which is the focus of this proposal. Using conditional ?knock-out? mice for both Tim 3 and Bat-3 in DCs, we propose to determine whether resistance to autoimmunity in Bat-3 cKO mice is partly or completely restored by deletion of Tim 3 from the same set of DCs. Furthermore, this will also allow us to determine how loss of Bat-3 regulates DC phenotype and function. 2. Determine the molecular mechanism by which interaction of Tim 3 and the Smad/TGF-b pathway promotes the generation of tolerogenic DCs. Using an unbiased proteomic screen to identify molecules that bind to the Tim 3 tail in the absence of Bat-3, we identified Smad-2, a transducer of TGF-b pathway, as a Tim 3 interacting protein. This novel observation allows us to study the mechanism by which Tim 3 mediates its inhibitory function, specifically we will be able to determine the molecular basis by which Tim 3/Smad/TGF-b pathway promotes the development of tolerogenic DCs. Using high density temporal transcriptional analysis of the Tim 3 and Bat-3 deficient DCs, we propose to develop transcriptional networks by which the Tim 3:Bat-3 pathway mediates its inhibitory function in DCs. The proposed studies will identify how the Tim 3:Bat-3 pathway makes DCs tolerogenic, providing critical information that could be exploited to benefit multiple human diseases. While repressing Tim 3 function could augment immune responses in chronic viral infections and cancer, boosting Tim 3 signals could dampen autoimmune diseases and promote antigen specific tolerance.